Controlled Access. Restriction lift date: 2028-09-30
Structuring alternative proteins extracted from grass and other alternative forages for food applications
Loading...
Files
Date
2024
Authors
Pérez-Vila, Sara
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
The current production system, and associated portfolio, for protein will soon be insufficient to meet the demand of the growing world population, so there is a need to explore alternative sources of proteins. Green leaves are a promising source of proteins due to their high content of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which is a photosynthetic enzyme and the most abundant protein in nature. However, to use it in our diet, the protein needs to be released from indigestible fibre in green leaves, concentrated and anti-nutritional factors be removed. This thesis focuses on the extraction of the soluble fraction of leaf proteins (mainly constituted by RuBisCO), studying their applications as functional food ingredients and assessing their nutritional value.
Different green leaves were explored as potential biomass sources for the extraction of soluble leaf proteins, and after this preliminary screening, perennial ryegrass and quinoa leaves were selected. Specifically, perennial ryegrass (Lolium perenne L.) was employed due to its abundance in Ireland and relevance for the Irish bio-economy. Two different extraction methods were compared to produce grass protein concentrates (GPC), differing in the application of a heating step, which improved the removal of the insoluble residues of chloroplast material. GPCs presented a crude protein content of up to 76% on a dry basis. The protein concentrate free of chloroplast material presented better solubility, up to 90% at pH 7, and had excellent emulsifying properties, comparable to those of whey protein isolate (WPI) at non-acidic pH. On the other hand, the protein extract containing residual chloroplast material was obtained with a higher extraction yield (sevenfold higher than when the heating step was applied), but its solubility was around 40% lower, which limited its performance as an emulsifier. Therefore, the extraction process applied significantly impacted the techno-functional properties, and the final application should be considered in the selection of the extraction process.
Additionally, quinoa leaves (Chenopodium quinoa W.) were also studied as a protein source, since they are currently a waste material from quinoa grain production, and it can be harvested in different parts of the world with the added benefit of producing the protein locally. Four different varieties of quinoa leaves (two grown in Ireland and two grown in Chile) were selected to produce protein extracts, and the presence of RuBisCO in them was confirmed by MALDI-TOF-TOF. The protein extract produced from Chenopodium quinoa Zeno (QPC) presented the highest solubility (90% at pH ≥ 5), which was attributed to the highest content of RuBisCO and lowest content of chlorophyll and phenolic compounds. QPC was further studied to formulate solid food hydrogels. By heat treatment at 95⁰C for 30 min at neutral pH, QPC was able to produce heat-set gels with a lower critical concentration of 10% protein, which was lower than that of WPI and soy protein isolate (SPI) under the same conditions. On the other hand, by adding 1.5% glucono-δ-lactone, QPC produced acid-induced gels with a porous structure, which has the potential to be a promising alternative to casein in the formulation of plant-based dairy analogues.
Finally, the nutritional quality of the three protein extracts produced (GPCs and QPC) was studied using the international consensus INFOGEST static in vitro digestion method. The protein extracts presented a high digestibility, over 97%, independently of the starting material, extraction method and application or not of a cooking treatment. Therefore, the GPC with poorer functional properties could still be used as a source of balanced protein to enrich food formulations, while the extracts with good functional properties could be introduced not only as a source of proteins with high nutritional quality, but also as functional ingredients.
In conclusion, the new scientific findings presented in this thesis constitute a significant advancement in the understanding of functional properties and nutritional value of protein extracts from green leaves.
Description
Controlled Access
Keywords
Plant proteins , RuBisCO , Green leaves , Techno-functional properties , Nutritional value
Citation
Pérez-Vila, S. 2024. Structuring alternative proteins extracted from grass and other alternative forages for food applications. PhD Thesis, University College Cork.